The Impact of Acid Mine Drainage on the Water Quality of the Odiel River (Huelva, Spain): Evolution of Precipitate Mineralogy and Aqueous Geochemistry Along the Concepción-Tintillo Segment

Abstract

The Odiel river emerges in Sierra de Aracena (N Huelva, Spain) as a clean, circumneutral river which shows abundant fish and fluvial microfauna. At 20 km from the riverhead and along a 7 km-long reach, this river receives four small discharges of acid mine water emanating from several abandoned mines of the Iberian Pyrite Belt (namely, Concepción, San Platón, Esperanza and La Poderosa-El Soldado). During two field studies performed in October 2003 and May 2004, it has been observed that these acidic waters (with flow rate of 0.2-8.5 L/s and pH 2.3-2.8) transfer to the Odiel river significant amounts of acidity and dissolved metals (specially Fe, Al, Mn, Cu, Zn, Cd, Co and Ni) and sulphate. Despite this mine-related pollution, the pH of the river remains near-neutral (pH = 7-8, flow rate = 220-1,000 L/s), as the alkalinity of the river (108-155 mg/L CaCO 3 eq.) neutralizes the acidity and causes the precipitation of dissolved Fe and Al in the form of ochreous to whitish minerals (ferrihydrite, Al-oxyhydroxides). These poorly crystallized minerals retain, by sorption (including adsorption and coprecipitation), large amounts of trace metals (specially Cu and Zn). Subsequently, the Odiel river converges with the acidic Tintillo river (pH = 2.5-2.8, flow rate = 48-240 L/s), which drains a vast mining area occupied by large waste-rock piles and tailings impoundments around Corta Atalaya (Riotinto mines). At this confluence, all the alkalinity is totally consumed and the pH drastically decreases to around 3. The mineral paragenesis of the ochreous precipitates is then dominated by schwertmannite, which shows a very limited sorption capacity under such acidic conditions. Consequently, metal concentrations are sharply increased from near-zero to tens of mg/L (e.g., 18 mg/L Fe, 76 mg/L Al, 14 mg/L Mn, 10 mg/L Cu, and 20 mg/L Zn in May 2004). The buffering capacity of the Fe(III) hydrolysis stabilizes the pH of the Odiel river around 3 ± 0.5 along the rest of its course to the Huelva estuary, and the water quality of the river is thus irreversibly damaged.

Iron terraces in acid mine drainage systems: A discussion about the organic and inorganic factors involved in their formation through observations from the Tintillo acidic river (Riotinto mine, Huelva, Spain)

“…1), which are also acidic and show comparable fl ow rates but lesser sulfate and metallic content. Finally, the Tintillo River converges with the Odiel River, causing a strong environmental impact on the latter and a sharp decrease of its water quality (Sánchez-España et al, 2005c, 2006a.…”

Monitoring study of the mine pond reclamation of Mina Concepción, Iberian Pyrite Belt (Spain)

“…In this sense, several recent works dealing with contributions of acid waters derived from mining activity in the province of Huelva to the watercourse of the river Odiel have been carried out (e.g. Sánchez-España et al 2006. The river Odiel presents a major contribution of acid waters in its sections located downstream from the studied area, as these sections are affected by the mining extractions of Riotinto.…”

Pollutant transport processes in the Odiel River (SW Spain) during rain events

“…Therefore, it is hypothesized that the Odiel River hydrochemistry evolved over the survey through mixing processes of these lixiviates and freshwaters. This hypothesis arises from the natural attenuation processes observed in the Odiel River up to the confluence of the Agrio River (also known as Tintillo), which collects Riotinto lixiviates, causing the irreversible deterioration of the Odiel water quality [ Sánchez‐España et al , 2006; Sarmiento et al , 2009]. In order to confirm this hypothesis, we simulated a mixing model performed with the MIX code [ Carrera et al , 2004] using as end‐members, the hydrochemical data of Riotinto lixiviates and the Villar Creek before receiving mine lixiviates (Table 3), the latter is an example of a freshwater representative of this catchment.…”